This invention is directed to a system for fabricating composites, and is particularly concerned with the provision of a system and method for producing composites, and particularly for repair of structurable members, wherein a component of the final composite functions as a heating element, for example in the form of a patch, to integrally bond such heating element or patch to a component of the composite or parent structural member.
A problem associated with the secondary or vacuum bag curing of composite materials is the introduction of heat to the materials to be cured, for example during repair of a structural component. Present practice involves the application of a heating blanket to cover the area to be cured or repaired, as well as structures in the vicinity of such area as determined by the size of the heating blanket. The resultant "global" effect of such large area heating has resulted in unsatisfactory curing of the composite and repair induced damage to a component due to the difficulty of maintaining constant and uniform heat distribution over such large area, especially in the presence of metallic parts.
Further, where a structural component, e.g., of an aircraft, and formed of molded plastic, metal or other material, requires repair, as by application of a patch to the damaged area, the necessity for using a heating blanket for bonding such repair patch to the structural component has also complicated the repair procedure due to the necessity of using the correct size and number of heating blankets to assure adequate heat distribution.
U.S. Pat. No. 4,250,398 discloses a unitary, composite laminate or sandwich structure used as a radiant heating device or heating blanket, and a method of producing the structure. The composite comprises an electrically insulating top and bottom layer surrounding an electrically conductive layer composed mainly of carbon, and is capable of emitting electromagnetic radiation when an electric current is passed therethrough.
U.S. Pat. No. 4,284,451 discloses a method and an apparatus for tire repair wherein flexible heating pads are applied to both the inside and outside of a patch area of a tire casing, and held in place under equalized pressure against the patch area by inflatable means. An electrical power source when used in conjunction with an inflatable air bag applies sufficient heat and pressure to patch the defective area.
U.S. Pat. No. 4,409,270 discloses a method for repairing surface defects in a cured, molded fiberglass reinforced plastic, primarily for cosmetic repairs and not structural type repair, wherein an external heating mat is employed and the repair material is electrically conductive.
U.S. Pat. No. 3,900,654 discloses a composite polymeric structure used as an electric heating element. The electrically conductive layer is formed of an electrically conductive elastomeric material made by mixing a fluoroelastomer with a conductive carbon black, and conductor means for electrically connecting the structure to a power supply.
Other prior art patents involving the use of carbon materials as external heating elements include U.S. Pat. Nos. 3,859,504; 3,277,419; and 2,489,643. All of these patents involve some form of resistive heating to produce heat which is generally thermally conducted into the desired areas.
In summary, the prior art patents as exemplified above involve external heating application only, that is the use of heating pads, blankets and panels.
Accordingly, one object of the present invention is the provision of a system for producing a composite or laminate wherein one or more elements or layers of the composite functions as a heating element or elements for curing the composite.
Another object is to provide a system and method for producing a cured composite, particularly wherein the parent material is a structural component, e.g., of a resinous material, which has been damaged and requires repair, and wherein an element or patch to be bonded to the parent material to form a composite has means incorporated therein which functions as a heating element or elements to effect such bonding.
A still further object is the provision of a system and method as noted above, for producing an integral cured composite, employing a heating element which is electrically conductive, and wherein reduced electrical energy requirements are achieved as compared to conventional heating for integral bonding of a heat curable layer or an element to a parent material.